Entropy is a concept that’s crucial to chemistry and physics. It helps explain why physical processes go one way and not the other. (5:19 min)

One of the most amazing facts in physics is that everything in the universe, from light to electrons to atoms, behaves like both a particle and a wave at the same time. But how did physicists arrive at this mind-boggling conclusion? Learn how in this video. (4:51 min.)

Your smartphone, tablet and other devices emit large quantities of blue light wavelengths. This tells your body "wake up!" when you should be getting ready to sleep. (2:50 min.)

It’s in our tap water, toothpaste and even in tea. Fluoride has helped reduce cavities in children for decades. Still, more than 70 years after Grand Rapids, Michigan, became the first city to fluoridate its drinking water, the practice remains controversial. Some worry that fluoridated drinking water can lead to health issues, but what is the scientific consensus? (3:14 min.)